1. Field of the Invention
The invention relates to the transfer of energy between a locus in a borehole and a subterranean formation penetrated by the borehole. In one aspect, the invention relates to formation of a structure for the recovery of heat from the geothermally heated formation by drilling a well, fracturing and propping with a slurry capable of maintaining a thermit reaction, igniting the slurry, and allowing to cool to form a conductor fin network within the formation for the conduction of heat to the locus in the wellbore. In another aspect, the invention relates to a heat recovery process for the recovery of heat from a geothermally heated subterranean formation comprising drilling a borehole into the formation, fracturing the formation with a slurry capable of maintaining a thermit reaction, igniting the slurry, allowing the molten metal formed by the thermit reaction to cool forming a metal conductor fin network from the bore into the fracture formation, and recovering heat conducted to a locus in the bore by a fluid heat recovery system.
2. Brief Description of the Prior Art
Many regions are known in which volcanic or intrusive activity has occurred recently enough so that the geothermal gradient is still as high as 150.degree. to 190.degree. C per km (435.degree. to 550.degree. F per mile). In such regions, temperatures high enough to produce commercially useful steam exist within two to three kilometers (6600 to 9800 feet of the earth's surface. In some places, natural steam can be produced from the geothermal heat.
Where natural steam is not produced, exploitation of such geothermal reservoirs has not been commerically undertaken, in spite of the fact that many of such reservoirs are closer to the earth's surface than are the lower levels of a deep mine. A principal reason for such lack of commercialization is because the thermal conductivities of the heat bearing rocks are typically very low. Though specific heats are high, so that a relatively large amount of heat is available from a unit volume of hot rock. Such heat, however, can be extracted from the rock only though some free surface such as a wall of a borehole. Since heat is conducted to that surface quite slowly, because of the low thermal conductivity of the rock, it is very difficult to remove thermal energy from the rock at a usefully high rate.
One approach to the problem of removing heat energy from such geothermal formations at useful rates is disclosed in U.S. Pat. No. 3,786,858 wherein a relatively large surface area is created by hydraulically fracturing between two well bores penetrating the geothermal formation and passing a fluid through the hydraulically created fracture system.
U.S. Pat. No. 3,857,244 discloses an advanced system for heat energy recovery from geothermally heated rock formations once the heat is transferred to a locus in the well bore adjacent to the geothermally heated rock.
U.S. Pat. No. 3,105,545 discloses injecting a slurry of metal particles into fractures formed in a hydrocarbon bearing formation to emplace closely packed metal particles in the fracture zone with subsequent circulation of heated fluid into the well to impart heat to the formation and provide for improved recovery of hydrocarbons.
My invention constitutes a substantial advance in the art by providing for efficient transfer of energy between a locus in a borehole and a subterranean formation. In a particular aspect, my invention provides for more efficient recovery of heat from a geothermal formation by overcoming the lack of sufficient thermal conductivity of the reservoir rock for feasible heat extraction.